To answer your question, let's talk about what
mountain building is. Mountains form where 2
tectonic plates converge -- they move towards each
other, collide, and sometimes they thrust upwards
to make mountains. This happens VERY slowly.
Even the fastest plates move only a few inches
each year, but over millions of years, this
movement builds up to mountains. So plate margins
and mountain events are the creation of mountains
where there might have been only flat lands
before. Talk about changing the landscape!

Answer 2:

There is nothing in geology called a "mountain
event". Mountains form as a result of two
processes: (1) faulting, by which rocks
slide past each-other, pushing up mountains as a
result of rocks bunching up, and (2) volcanic
activity, which creates mountains out of the
frozen lava that gets expelled from the vent.